The present invention relates to additive formulations, particularly for fuels, comprising at least one alkoxylated imidazo-oxazole compound, at least one compound selected from the group formed by detergent-dispersant products and at least one product selected from the group formed by mineral or synthetic lubricating oils and polyglycols which are soluble in said fuel. These formulations may be used as multifunctional additives for fuels used in internal combustion engines, in particular spark ignition engines.
Use of conventional fuels often results in coking of engine parts due to incomplete vaporisation and combustion of the fuel in the intake system and combustion chambers.
When using spark ignition engines in particular, the formation and accumulation of deposits in the combustion chambers adversely affects the normal operating conditions of the engine.
These deposits significantly affect thermal exchange between the combustion chambers and the engine cooling system by forming an insulating layer.
This results in an increase in the temperature in the chambers to which the gas mixture is submitted. This encourages self-ignition of these gases, and the well known phenomenon of pinging then occurs.
In addition, accumulation of deposits in the combustion chambers can reduce the volume of the combustion zone leading to an increase in the compression ratio of the engine. This can also encourage pinging. Further, the deposits formed in the various engine parts which come into contact with the fuel can partially absorb a portion of the fuel and thus change the oxidant-fuel mixture resulting in a fuel depleted phase during absorption and an enriched phase during fuel desorption. If the fuel-air mixture is altered, the engine can no longer operate under optimal conditions.
Coking can be removed by periodic cleaning of the elements affected, in particular the valves. This is particularly onerous.
Accumulation of deposits in the engines, in particular on the intake valves, can also be reduced by employing fuels containing certain additives, for example detergent type additives which may be combined with anticorrosive or antideposit additives for the combustion chamber, for example.
Additives are well known industrially, for example polyisobutene-amine type additives, normally associated with a mineral or synthetic oil. They can lead to increased coking in the combustion chambers and thus an increase in the octane requirement of the engine with a greater sensitivity to pinging.
Examples of prior art additives are the condensation products of polyalkenylsuccinic anhydrides with polyamines such as, tetraethylenepentamine, which are particularly described in U.S. Pat. No. 3,172,892. These additives exhibit good anticorrosive properties but are not effective as valve detergents.
Condensation products of polyalkenylsuccinic anhydrides with hydroxyimidazolines, in particular 1-(2-hydroxyethyl)imidazolines substituted in the 2 position by an alkyl or alkenyl group, may also be cited. These are described, for example, in European patent application EP-A-74 724. The products described in this application are good engine fuel additives and exhibit good anticorrosive properties, but are not very carburettor cleaners.
Coking of the combustion chambers occurs progressively during engine operation. This is characterised by its octane requirement which corresponds to the minimum octane number of the fuel required in the engine for it to operate without pinging. When the octane requirement exceeds the octane number of the fuel supplied to the engine, particularly when the combustion chambers are coked, pinging occurs. The increase in the octane requirement of the engine is known to the skilled person as ORI or "Octane Requirement increase".
The onset of pinging and its onerous consequences such as fatigue and increased wear of essential parts can be limited by avoiding too high an octane requirement by using a higher octane fuel than previously used, provided this is available and the higher costs can be tolerated. The combustion chambers can also be cleaned periodically to eliminate the deposits formed and reduce the engine octane requirement. This operation is, however, long and expensive.
Many patent documents describe additives for particular use in engine fuels. Compositions such as those described in European patent EP-A-327 097, for example, exhibit good anti-ORI properties but have relatively limited detergent properties. In addition, these compositions are not described as exhibiting good anticorrosive properties.